1. Field of the Invention
This invention is related to light emitting diode (LED) light extraction for optoelectronic applications. More particularly, the invention relates to an (Al, Ga, In)N and ZnO structure combined with optimized optics for highly efficient (Al, Ga, In)N-based LED applications, and its fabrication method. A further extension is the general combination of a shaped high refractive index light extraction material with a shaped optical element.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification. A list of these different publications can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Wafer bonding technology using different combinations of materials, such as InP/GaAs, AlGaInP/GaP, GaAs/GaN, ZnSSe/GaN, has been studied for applications such as optoelectronic integration, light emitting diodes (LEDs), vertical cavity surface emitting lasers (VCSELs), and electronic devices [1-4].
In a nitride LED system, there are several reports of fabricating transparent electrodes on a p-type gallium nitride (GaN) layer. The general method is to use thin metals of nickel (Ni) and Gold (Au) [5]. However, because of the light absorption in the metal, transmittance is only around 60%. Also, surface feature shaping for improving light extraction efficiency is difficult because of the hardness of GaN material and the instability of p-type GaN conductivity.
Another approach is to use zinc oxide (ZnO) layer growth on p-type GaN [6]. However, this method requires ZnO crystal growth equipment, which uses ultra-high vacuum conditions. Moreover, it is difficult to grow thick layers, e.g. 500 μm thick layers, that are suitable for feature shaping for the purpose of light extraction.